Effect of dopant concentration and annealing of Yttrium doped CuO nanocrystallites studied by positron annihilation spectroscopy

Abstract

In this paper, we report the solution combustion synthesized Yttrium doped CuO nanocrystallites studied by positron annihilation lifetime (PAL) and Doppler broadening (DB) spectroscopy. The lattice defect in Y doped CuO nanocrystallites is presented by the effect of dopant concentration and annealing temperature. X-ray diffraction measurements indicated monoclinic CuO with impurity phase (Y2O3) of Y at elevated temperature. Scanning Electron Microscopy observations showed the particles are more agglomerated upon annealing. The PAL study exhibited three-lifetime components (τ1, τ2, and τ3) wherein, as-prepared CuO exhibited an increased lifetime (τ1) of 212 ps compared to the reported bulk lifetime of 169 ps. The analysis confirmed the mixed contribution of the annihilations of trapped positrons in CuO bulk, point, and extended defects. The τ2 and τ3 are ascribed to the vacancy clusters and voids. Defects modification with doping concentration and annealing temperature are explained in detail. The average positron lifetime (τav) of all the samples increases with doping concentration and decreases with annealing temperature. Grain growth hindrance due to Y ion migration is presented effectively, signifying the higher average lifetime. Comparative analysis of the average lifetime with the extracted from the valance electron annihilations associated S parameter from DB and on the crystallite size variation with annealing is presented on the basis of defects formation and its curing mechanism. The defect structure change owing to charge compensation of Y in CuO is explained. The defect modification of doped and annealed CuO is explained well from the change in crystallite growth and surface defects.